The following discussion of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge (in any country) as at the priority date of any of the claims.
The banana plant is a large perennial herb with leaf-petiole sheaths that form generally cylindrical, trunk-like pseudostems. Each pseudostem grows from a bud on the true stem (corm), which is an underground rhizome, and can grow to heights normally in the range of 3 to 8 meters over a 9 to 18 month period. When mature, the pseudostem will comprise a soft but dense centre (a ‘core’) surrounded by an outer layer (a ‘sheath’) that is tougher but is less dense, the outer layer typically being formed by the overlapping leaf-petiole sheaths.
Commercially planted banana plants typically only have 1 to 2 year life-spans, as banana plants only flower (and produce bananas) once, following which the leaves, leaf stalks and pseudostem start to die. This usually requires their removal in some manner, such as by simply being cut down, allowing regrowth of a new pseudostem from the rhizome and the commencement of a new reproductive phase.
With annual production in 2002 of about 68 million tonnes of bananas (more than two thirds coming from within India, Brazil, China, Ecuador and the Philippines), it has been recognised that banana pseudostems represent a potentially valuable renewable resource, one which has been traditionally under-utilised and historically economically ignored by banana growers. With this in mind, there have been numerous attempts to use the pseudostems for the production of paper, due to the beneficial properties and qualities of the fibre in the pseudostems.
However, in a paper titled “Banana Stem Fibre for Papermaking” by S. K. Singhai, J. K. Garg and B. Biswas for the Indian Pulp and Paper Journal, August-September 1975, 30(2), pp 13 to 15, the situation at that time was summarised as “The pulping and papermaking qualities of banana (M. sapientum and M. paradisica) stem fibre have been examined. From the available information given in this paper, it is to be considered that neither technically nor economically the use of banana stem fibre is a feasible proposition.” Thus, at least in the mid 70's, no sensible approach had yet been developed to the use of these materials for paper production.
Since then, it has continued to be recognised that banana pseudostem fibres should have suitable properties for paper production. In a paper titled “Plantain (M. Paradisiaca L) Pseudostem; A Fibre Source For Tropical Countries” by Nicholas A Darkwa of the Forestry Research Institute of Ghana, published in Book 2, TAPPI Proceedings, 1998 for the 1998 Pulping Conference in Montreal Quebec, it was concluded that “ . . . tropical countries that are deficient in long-fibred material for their pulp and paper production can utilise the pseudostems of plantain and banana for such purposes.”
Indeed, several attempts have been made to use banana plant refuse (predominantly pseudostems, but including leaves, leaf stalks, immature inflorescence and unused bananas) in existing or modified paper pulping processes—see U.S. Pat. No. 5,958,182 for a short summary of some such processes.
However, such refuse commonly has an extremely high water and natural latex content, and includes numerous resinous and gummy substances that are difficult to handle and process. In order to produce workable fibres having desirable characteristics for paper-making, it has proven necessary to extract these fluids and, in particular, wash out the latex and other natural resinous substances. This has proven to be technically difficult, and has generally made the pulping of banana refuse for the production of paper uneconomic, particularly for bulk paper supplies and for anything other than boutique or artistic papers. It has also generally presented the manufacturers with significant chemical waste disposal issues.
In Australia, while it has been reported that a good quality paper can be made in low volume by combining banana fibre with that of the betel nut husk (Areca catechu L.), Australian investigators have still concluded that the yield of banana fibre is too low for extraction to be economical. It has been reported that only 1 to 4 oz (28-113 g) of suitable fibre can be obtained from 40 to 80 lbs (18-36 kg) of green pseudostems from the pulping process. Thus, 132 tonnes of green pseudostems would yield only 1 tonne of paper. The conclusion was that the pseudostem would have much greater value as organic matter chopped and left in the field to fertilise subsequent crops.
The present invention seeks to provide a method that makes possible the use of banana plants in the family Musaceae for the production of sheets useful in the production of raw paper for subsequent conversion to paper products, ideally in a manner that is both technically simple and reasonably economic, so as to permit relatively high volume paper production therefrom.